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Where Do Blood Cells Come From?

In the post on TNF inhibitors, we took a look at the white cells listed on a Complete Blood Count with differential.

Unfortunately, a discussion of white cells isn’t quite so straightforward. There are actually a few different explanations of white cells and their behavior, and I suspect that if scientists really had all the answers, things would all fall in place and be much clearer than the current model.

All blood cells are formed from stem cells in the bone marrow. It’s believed that the specific type of blood cell formed depends on which chemicals act on the stem cell. By way of analogy, think about sperm & egg coming together – if the sperm contains a Y-chromosome, a boy develops; if the sperm contains an X-chromosome, a girl develops. Same egg, but the end product varies depending on what it comes in contact with. With that in mind, we return to cell development. Stem cells that are acted on by interleukin-7 become lymphocytes (a kind of white cell); if they encounter a different chemical, they become a different type of cell.

I’ve found a number of similar theories as to which chemicals (cytokines & hormones) lead to the development of different types of cells.

Obviously the cell-development theory still needs work. There’s a hole in the theory when natural killer cells are sometimes included and other times ignored (and then dendritic cells are tossed in as an afterthought, without any explanation). It’s inelegant to sometimes group white cells 3-2 and other times group them 4-1 unless there’s a very good explanation of how those differences influence their behavior. In other fields of study, when it’s not clear how something works (or if there are big exceptions to the theory), it means you haven’t yet figured out the right solution yet. I believe this is true with what we know about cell development.

Be that as it may, a future post will investigate some of the cool things that white cells do, and how this knowledge influences RA treatment.

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9 thoughts on “Where Do Blood Cells Come From?”

Nice that you’re doing some posts on this for laymen. I tried semi-looking into this in the distant past, but suppose I got confused at some point and gave it up, not knowing the best sources to turn to that didn’t cost any money anyway. Is this arising in part from homeschooling?

Anyway, in regards to this sentence,
“It’s inelegant to sometimes group white cells 3-2 and other times group them 4-1 unless there’s a very good explanation…”

Not related to homeschooling, but I did use our A&P text as one of my sources.

3-2: Of the five main types of white cells, three kinds are granulocytes (cells with granules in the cytoplasm). There are two kinds of white cells that are agranulocytes (cells without granules).

4-1: Of the five main types of white cells, four develop from GM-CSF influencing the stem cell; one kind of white cell develops differently.

Based on what I know of other scientific fields (and other areas of study), I believe that the “right” explanation will simply and elegantly say “this group of cells all develop like this, and that group develops like that, that’s why this group all have these similar features/behaviors and that group all have those similar features/behaviors.” The current theories about white cells aren’t anywhere close to such a straightforward explanation.

I have been reading your blog for a while and I just wanted to give a little insight into the blood cell development, beyond the A&P textbook, which is out of date before it even gets published – science just moves so fast right now.

Not every type of WBC develops from the same precursors. So GMCSF can act on one precursor to produce one type of cell, and can act on a different precursor to produce different cells. This is also very simplified – when and for how long the growth factors are acting on the cells also determine what mature cell will develop.

As an aside, dendritic cells are a fairly exploding area of current research and you are absolutely correct that the jury is still out on their role and develop, but I am sure that they are related to RA disease activity.

As another addendum (immunology is a big area of interest for me), there’s yet another group of cells called Mast Cells which aren’t included on your diagram (these are the guys who can help fight parasites along with eosinophils and release histamine and other cytokines which cause anaphylactic reactions).

The likely reason they’re not on there is that we know NOTHING about how they develop. Seriously, go look at this chart ; the mast cells just kind of teleport in at the bottom.

When monocytes leave the bloodstream and enter tissue, they morph into macrophages, so that’s a type of white cell that’s not found in the bloodstream and I’ve not mentioned before (I want to do a whole post on macrophages, which are another producer of TNF, but don’t understand them enough to do even an introductory post yet). Dendritic cells need to be added, as do Natural Killer cells. That’s all I know of so far, but who knows what future research will turn up.

I’d thought of pulling in more resources and making one giant, all-inclusive chart, but the chart that Not House linked looks like what I’ve been looking for so I’m inclined to just direct everyone there.

There are other types of cells, but I started off thinking about how the immune system works (or malfunctions), then expanded to what can be learned from labwork. In addition to macrophages, there are other cells that also develop from monocytes.